| 1. |
- Johannesson, Henrik, 1953, et al.
(författare)
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Conformal field theory approach to the two-channel Anderson model
- 2004
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853. ; 272-276:SUPPL. 1
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Tidskriftsartikel (refereegranskat)abstract
- The two-channel Anderson impurity model serves as a prototype for describing heavy-fermion materials with a possible mixed-valent regime with both quadrupolar and magnetic character. We report on the low-energy physics of the model, using a conformal field theory approach with exact Bethe Ansatz results as input.
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| 2. |
- Weissenrieder, Jonas, et al.
(författare)
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Experimental evidence for a partially dissociated water bilayer on Ru{0001}
- 2004
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 93:19
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Tidskriftsartikel (refereegranskat)abstract
- Core-level photoelectron spectra, in excellent agreement with ab initio calculations, confirm that the stable wetting layer of water on Ru{0001} contains O-H and H2O in roughly 3:5 proportion, for OHx coverages between 0.25 and 0.7 ML, and T<170 K. Proton disorder explains why the wetting structure looks to low energy electron diffraction (LEED) to be an ordered p(root3xroot3)R30degrees adlayer, even though approximate to3/8 of its molecules are dissociated. Complete dissociation to atomic oxygen starts near 190 K. Low photon flux in the synchrotron experiments ensured that the diagnosis of the nature of the wetting structure quantified by LEED is free of beam-induced damage.
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| 3. |
- Karlsson, Krister, 1961-, et al.
(författare)
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Spin-wave excitation spectra of nickel and iron
- 2000
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Ingår i: Physical Review B Condensed Matter. - : American Physical Society. - 0163-1829 .- 1095-3795. ; 62:5, s. 3006-3009
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Tidskriftsartikel (refereegranskat)abstract
- A Green’s function formalism for calculating spin-wave excitations is developed for practical calculations and tested for real solids. The mapping to the Heisenberg Hamiltonian commonly used in spin-wave calculations is avoided, making the formalism suitable for both localized and itinerant magnetic systems. To test the formalism, we have calculated the spin-wave spectra and dispersions of ferromagnetic Fe and Ni. The results prove to be in very good agreement with experiment and some novel features are predicted.
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| 4. |
- Schröder, Elsebeth, 1966, et al.
(författare)
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The van der Waals Interactions of Concentric Nanotubes
- 2002
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Ingår i: Proceedings of NANO-7/ECOSS-21.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Concentric nanotubes are stabilized by a competition between the short-range repulsion andthe long-range van der Waals binding. At the relevant binding distances (3.4 Ångström) wefind that traditional first-principle density-functional theory (DFT) calculations can only par-tially account for these combined interactions and that an accurate quantum-physics accountof structure and dynamics must also include a calculation of the van der Waals forces. We usea successful model of the electrodynamical response of the nanotube electron gas to providesuch a combined description in which we reflect the important self-consistent screening effectsarising within the nanotube electron gases. Our description differs significantly from traditionalasymptotic calculations of the van der Waals interactions. Work supported by the Carl Tryggers Foundation, W. and M. Lundgren Foundation, the Swedish Research Council (VR), andthe Swedish Foundation for Strategic Research (SSF).
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| 5. |
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| 6. |
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| 7. |
- Sjögren, Lennart, 1947
(författare)
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Regenerative processes in supercooled liquids and glasses
- 2003
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Ingår i: Physica A. - 0378-4371. ; 322, s. 81-117
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Tidskriftsartikel (refereegranskat)abstract
- The mode-coupling equations used to study glasses and supercooled liquids define the underlying regenerative processes represented by an indicator function Z(t). Such a process is a special case of an alternating renewal process, and it introduces in a natural way a stochastic two level system. In terms of the fundamental Z-process one can define several other processes, such as a local time process Image and its inverse process T(t)=sup{u : H(u)less-than-or-equals, slantt}. At the critical point Tc these processes have ergodic limits when t→∞ given by the stable additive process Ya(t) and its inverse process Xa(t), where a is the critical exponent. These processes are selfsimilar, and the latter is given by the Mittag-Leffler distribution. The appearance of these limit processes, which is a consequence of the Darling–Kac theorem, is the generic reason for the universal predictions of the mode-coupling theory, and are observed in many glassforming systems. We also find a similar behaviour for the α-relaxation function but for the initial behaviour at t→0, and the limit processes are in this case given by Y1−b and X1−b, where b is the von Schweidler exponent. This also implies that the relaxation function belongs to the domain of attraction of the stable distribution with the characteristic function exp(−tb).
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| 8. |
- Vestergren, Anders, et al.
(författare)
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Effect of columnar disorder on the superconducting transition of a type-II superconductor in zero applied magnetic field
- 2004
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 70:5
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the effect of random columnar disorder on the superconducting phase transition of a type-II superconductor in zero applied magnetic field using numerical simulations of three dimensional XY and vortex loop models. We consider both an unscreened model, in which the bare magnetic penetration length is approximated as infinite, and a strongly screened model, in which the magnetic penetration length is of order the vortex core radius. We consider both equilibrium and dynamic critical exponents. We show that, as in the disorder free case, the equilibrium transitions of the unscreened and strongly screened models lie in the same universality class, however scaling is now anisotropic. We find for the correlation length exponent nu=1.2+/-0.1, and for the anisotropy exponent zeta=1.3+/-0.1. We find different dynamic critical exponents for the unscreened and strongly screened models.
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| 9. |
- Aleksandrovskii, A. N., et al.
(författare)
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Thermal expansion of single-crystal fullerite C60 at helium temperatures
- 2000
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Ingår i: Low temperature physics (Woodbury, N.Y., Print). - : AIP Publishing. - 1063-777X .- 1090-6517. ; 26:1, s. 75-80
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Tidskriftsartikel (refereegranskat)abstract
- The thermal expansion of single-crystal fullerite C60 has been studied in the range of liquid-helium temperatures (2–10 K). At temperatures below ~4.5 K the thermal expansion of fullerite C60 becomes negative, in agreement with the previous results on polycrystalline materials. A qualitative explanation of the results is proposed.
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| 10. |
- Arvanitidis, J., et al.
(författare)
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High pressure study of the 2D polymeric phase of C60by means of raman spectroscopy
- 2000
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Ingår i: High Pressure Research. - : Taylor & Francis. - 0895-7959 .- 1477-2299. ; 18:1-6, s. 145-151
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Tidskriftsartikel (refereegranskat)abstract
- The effect of high hydrostatic pressure, up to 12 GPa, on the intramolecular phonon frequencies and the material stability of the two-dimensional tetragonal C-60 polymer has been studied by means of Raman spectroscopy in the spectral range of the radial intramolecular modes (200-800 cm(-1)). A number of new Raman modes appear in the spectrum for pressures similar to 1.4 and similar to 5.0 GPa. The pressure coefficients for the majority of the phonon modes exhibit changes to lower values at P=4.0 GPa, which may be related to a structural modification of the 2D polymer to a more isotropic phase. The peculiarities observed in the Raman spectra are reversible and the material is stable in the pressure region investigated.
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